Lasing Phenomena in Mixed Random & Ordered Media

固态激光器，由于其传输信息的大容量，已经彻底改变了我们的沟通方式，极大地提高了我们的生活质量。这些激光器发展的主要挑战之一是完美和精确的薄膜晶体层的生长。因此，从固态激光器的发明到其商业化已经花费了几十年的时间。一个基本的、挥之不去的科学问题是，激光能否在完全无序（或随机）的介质中发生。如果是这样的话，激光的工作效率是否足够高？最近，研究人员发现他们可以在随机介质中实现相干激光。他们发现，无序诱导的光散射不仅为激光提供了相干反馈，而且还导致了激光在微米大小的随机介质中的空间限制。他们制造了一种新型的无序介质微激光器。然而，激光的阈值对于实际应用来说仍然太高。这种高激光阈值是由于光在随机介质中的不完全捕获造成的。在这个项目中，研究人员计划在随机介质中引入有序，以实现更好的光定位，从而降低激光阈值。该研究项目将着重于二维和三维部分有序随机介质中激光现象的实验和理论研究。这种激光介质由均匀排列的无序程度不同的ZnO纳米棒或纳米球组成。所提议的活动将从理论分析和数值模拟开始，以预测满足激光最佳条件的结构。采用最佳设计标准，激光器的纳米制造将在这些随机激光器的结构表征和光学测量之后进行。研究人员设想，他们提出的计划的成功将丰富学生，教师和他们的同事的研究和教育环境。特别是，他们预测他们的工作将在以下领域产生最大的影响：(1)应用于研究-由于低阈值随机激光器比单缺陷光子晶体激光器制造成本低得多，因此它可能是许多应用中的低成本替代品。(2)将研究与教育相结合——研究者在将教育与涉及大学预科学生、本科生和研究生的研究相结合方面拥有丰富的经验。他们将继续举行联合小组会议，在学生和研究人员之间讨论最近的研究成果。(3)科学内容和课程开发：基于美国国家科学基金会资助的材料世界模块的成功，研究者将参与开发一个动态的、定制的、基于网络的课程，为大学预科和本科一年级的学生提供“材料中的光波现象”领域的课程。光的反射，折射和散射的基本概念，从表面和纳米结构材料将讨论。他们将通过给出一系列工业应用和我们的环境中的例子来发展这些概念。此外，学生将学习如何在材料中产生、操纵和检测光的许多应用。本课程将基于网络，具有不同的难度。他们将与世界各地的同事合作，随时更新和修改内容。最后，这将是一个全球性的课程，有许多令人兴奋的贡献。(4)外展与全球传播——研究人员将在西北国际虚拟研究所（IVI）全球研究图库中发布研究成果，供公众观看。与拟议研究有关的讲座和研讨会将录成录像带，并储存在国际创新研究所的演讲厅，供其他人观看。(5)科学教师和代表性不足的学生的暑期研究项目——研究人员将继续在他们的实验室里接待科学教师和代表性不足的学生，进行由美国国家科学基金会资助的西北大学材料研究科学与工程中心赞助的暑期研究项目。

0244457CaoSolid state lasers, due to their large capacity to transmit information, have revolutionized the way we communicate, greatly enhancing the quality of our lives. One of the major challenges in the development of these lasers has been the growth of perfect and precise thin film crystal layers. Thus, the time between invention of the solid state lasers and their commercialization has taken several decades. A basic, lingering science question has been whether or not lasing can take place in a completely disordered (or random) medium. And, if so, would the laser operate efficient enough for applications? Recently, the investigators have discovered that they can achieve coherent lasing in random media. They found that disorder-induced light scattering not only provides coherent feedback for lasing, but also leads to spatial confinement of laser light in micrometer-sized random media. They fabricated a new type of microlaser with disordered medium. However, the threshold for lasing is still too high for practical use. This high lasing threshold results from incomplete trapping of light in the random medium. For the proposed project the investigators plan to introduce order into a random medium to achieve better localization of light, thus lowering the lasing threshold. The research program will focus on both experimental and theoretical studies of lasing phenomena in two-dimensional and three-dimensional partially ordered random media. Such lasing media consist of uniform arrays of ZnO nanorods or nanospheres with variable degrees of disorder. The proposed activities will start with theoretical analysis and numerical simulation to predict structures that meet the optimal conditions for lasing. Using the best design criteria, nanofabrication of lasers will take place followed by structure characterization, and optical measurements of these random lasers.The researchers envision that the success of their proposed program will enrich the research and education environment of students, teachers, and their colleagues. In particular, they foresee the following areas in which their work will deliver the most impact: (1) Application to research-Since a low-threshold random laser is much cheaper to manufacture than a single-defect photonic crystal laser, it may be a low-cost alternative in many applications. (2) Integrating research with education-The investigators have extensive experience in the integration of education with research involving pre-college students, undergraduates, and graduate students. They will continue to have joint group meetings where recent research results are discussed among the students and the investigators. (3) Science content and curriculum development-Based on the success of the NSF-funded Materials World Modules, the investigators will be involved with the development of a dynamic, customized, web-based course for pre-college and first year undergraduate students in the area of "light wave phenomena in materials". Basic concepts of light reflection, refraction, and scattering from surfaces and nanostructured materials will be discussed. They will develop these concepts by giving a series of examples from industrial applications and our environment. In addition, students will learn the many applications of how light can be generated, manipulated and detected in materials. This course will be web-based, with different levels of difficulty. They will collaborate with their colleagues around the world to up-date and revise the content any time. In the end this will be a global course with many exciting contributions. (4) Outreach and global dissemination-The investigators will post their research results in the Global Research Gallery of the Northwestern International Virtual Institute (IVI) for public viewing. Lectures and seminars relating to the proposed research will be video taped and stored in the Lecture Hall of the IVI for others to view. (5) Summer Research Program for science teachers and underrepresented students-The investigators will continue to host in their laboratories science teachers and underrepresented students to perform summer research programs that are sponsored by the NSF-funded Materials Research Science and Engineering Center at Northwestern University.